Telephone or like system



May 8, 1945.

D. CHRISTIAN ETAL TELEPHONE 0R LIKE SYSTEM Filed May 13, 1943 2 Sheets-Sheet 1 FIG. I

IDF

' INVENTORS David Adam Chrisflon Douglas Percy Long AT O EY y D. A. CHRISTIAN ETAL ,375,

1 TELEPHONE OR LIKE SYSTEM Filed May 13, 1943 2 Sheets-Sheet 2 Fl I continued INVENTORS David Adam Chrisflcm Douglas Percy Long ATTORNEY v Patented May 8, 1945 UNITED STATES ATENT OFFICE TELEPHONE on LIKE SYSTEM David Adam Christian, Batley, and Douglas Percy Long, Chislehurst, England, assignors to Siemens Brothers & Co. Limited, London, England, a British company ApplicationMay 13, 1943, Serial No. 486,784 I i h In Great Brita-in'June 3, 1942 i This invention relates to telephone systems andmoreparticularly to systems in Whichcall finders are employed. Whilst it is of general application to arrangements-in' which callfinders are assigned for use by allotters it is especially applicable to line finders concerned. with the connection of incoming lines to common'apparatus.

InY an automatic telephone systeme'mploying finders it is usual to group the "incoming lines and for each groupof lines to provide a group of finders of appropriate size and one ormore allotters to allot a free. finder to deal from an incomingline.

@In the case of subscribers lines: it has been found convenient to group two hundred lines.

with a call The number of call finders necessary for such a group will vary with the calling rate. It may I for example be 20, 23, 27 or 30. Two allotters would generally be provided for the group one It is commOn practice as regardsautomatic telephone exchange equipment to provide racks having a column of panels of tenswitches. Ac-

cordingly one would haveyior thefinder groups mentioned, to utilise at least two and for the largest group mentioned three panels. Where groups of 23 or 27 come'intoquestion three panels could be used but there would be spare space or spare banks not in use.

As a compromise, panels, so far as wiring is concerned have been sub-divided so that one may form groups of multiples of five. In some cases wider racks have been employed such as would accommodate twelveswitches' when the calling matter approached from the point of view of a rack.

In the present invention all the banks of all allotters on the" rack are multipled and outlets taken to all the'line finders so that an allotter has access to every finder for control purposes.. Since, however, an allotter eventually has only to deal with a particular group of line finder its testing-in circuit is so arranged that by strape ping or by the cutting of a strap connection it is enabled to. test into that group only. A convenient way of achieving this is to arrange that the test relay circuit of the allotter extends from the test wiper through a" test relay to a mark ing bank wiper." The connection to earth of contacts in themarking bank would permit only the testing of line finders corresponding to the earthed contacts.

The number of allotters provided depends primarily on the number of groups of line finders appearing in the rack but for standardisation one may provide the banks, if not the mecharate indicates that round about 24 finders.

should constitute a group.

It is one object of the present invention to provide a disposition and connection of line finders and allotters on a rack such that it can be a stock rack which maybe readilyadapted to the requirements of an exchange.

To this end the conception of a group of lines,

nisms,on .thebasis of one for each ten line finders. It may happen that the number of outlets from the allotters will exceed the number of line finders on the rack; for example, there may beseven panels of ten line finders each and the allotter is a hundred point switch. The 30 excess outlets could be used to serve line finders on another rack.

Therack is also adapted to be used in the following manner. Although the average calling rate for an exchange might dictate say 23 line finders for a groupof 200 lines which represents a loss of spaceTwherepanels of ten finders are standardised yct' thisaverage calling rate may be met so far as 600 lines are concerned by providing' twogroups of twenty line finders and one group of thirty line finders and assigning lines with lesser calling rates to the groups of twenty line finders and those with heavier calling rates to the group of thirty line finders. The strapping in the allotter already referred to provides the necessary] association of allotters with the different sized groups. v

It. will be apparent that by abandoning the arrangement of allotters associated by wiring only with a particular group of line finders and by multiplying them to alljfinders groups of line finders of varying size can readily be arranged in ny desired order' on a rack or can even overlap onto an adjacent rack. v

Of the line finders of a group some may be ungraded and others graded" or some may be directly connected to a selecting switch whilst men group or line finders.

ranged totest for the presence of battery poten tential a suitable source of potential may he pro,-

' vided, said potential being nullifiedwhen the line' finder is seized and the usual busy earth is ap plied to the test wire.

Where secondary line finders are used, these i may be mounted in panels and associated with allotters in a similar manner gto that described.

Relays for the control of primary finders may ape .1

pear on the secondary finder rack.

The line finders and allotters may "be high pee sing e motion sw t hes drivelhr n ividual driving motors and the allotter may be arranged so th t ai e one h s beenic e sed m a call. it pws le ts l ne; finder or 314 n-t e next cal The nature of this invention ,willib clear frQm assmsiena icn wot a s e ificemb diment given y Wa o examp e-a d taken in niun -tion with th aco pany li draw nss ich Fi l i a sc emat c d ag m o aline nd r a d as c at d il al ter.

Fi s, 2 and 2b sho the aimin em l y between terminals of different call allotters two ;or three .allotters, respectively, serve a cornliiighd shows modifications r quir d. n i where the line finder is oneof several graded finders which are-connected to a single first sel At. a telephone exchang -the line finders are arranged in racks, -,each racl; comprising a number'ofhhanels. horizontally disposed in verti al tiers. For the purpose of the example a rack will be assumed to. contain seven; panels oiline findersand a panel of allotters for their control.

Furthermore, each panel'of line finders will be ass. medto contain lojsw tche's all the switches of apa e ope a i g on the sam mult Eac line finder is provided with 2.00 outlets which -.,fo .-m a. g ou and a r p o in s wiu u ally need not less than Zpanls'of line finders for its adequate service. .Where two panels of line finders serve a single group ofv li es the line finder multiple will therefore extend'ove'r the two panels. If thre panels of line' finders are re qui ed to ve ad si ateha r u of lines the line finder multiple will accordingly extend over the three panels. The allotters will be provided at asu able a e. The will usua ly beat l ast tw'ojallotter's for each group of line finders and here, may be thr The allotters are' om ected to a'common multiple and '70 outlets in themultiple are connected to the '70 line'finders' onthe rack, one outlet to each linefinder. The. allotters are 100 outlet switches so there 'will be 30 outlets not" connected to line finders'on the rack.

a rack are not divisible into an exact number of groups but a group may comprise one or more panels of line finders on one rack and one or more panels of line finders on another rack. In order that all-the finders of a group so divided may be controlled by their respective allotters ,use is made of the additional outlets. For example, a rack-may have \on it one :.panel of a three panel group, the other two panel of line finders being accommodated on an adjacent rack. As 70 .outlets on the allotters are required for the '70 line finders on their own rack use is made of the '30 additional outlets for the control of the line .finders of the same group accommodated on the adjacent rack. Similarly use is made of the ad- :d-itional outlets on the allotters on the adjacent rackiorthe control of that part of a group that These may be connected to linefinders on an adjacent rack, It is arranged that an allotter is availab e fo use with any in fi e of a. g o p- Th s, if agroup consists of 20 line finders ac miodaie o wo, pane s and w al qt i rs are assis edflto t e g up e cha t r aybe Permitt'ed to control any of the201inefinders oi the roup or e. control x rc s d by t e otters me n rma i'fber st ciedw o on ane oiiline fi ders-fi m happen t at he i efinders n :is-nol accommodated on its own rack so that the rate of provision of allotters and. their accessi- -bilityto"-whole groups may be maintained.

The rate of provision of line finders usually depends on the average calling rate per line of all the lines .connected.to the exchange. This may and in'many instances would not be a number convenient to the efficient lay-out of line finders, that is it will not require a number of complete panels of line finders" for adequate service. It may, for example require 23 line finders ,per group. If the rack is constructed to hold panels of 10 lin finders obviously much space will be wasted an'ol unnecessary provision of apparatus involved since the multiple will extend over the whole panel and the banks, at least, of the full number of line finders Will be fitted and wired ,to the multiple. If recourse is had to half panels the advantages of a standard size of rack is lost Accordingly, it is proposed to re-group the lines,

allotting the more heavily loaded lines to one rate of 23 per group of 200 lines averaged over 3- .groups; "This provision .of two groups of 20 line finders and-one gr up f 30 may be repeated as often .as necessary. In this particular example, it happens that the finders ofthe combined groups occupy a complete rack butit :notnecessary thatthis should be so. For instance, the smaller gr ups c uld e to ether on one set of racks and the r er s upscnanother s t- It will now be explained, by reference to the accompanying drawings, how the association of the allotters and line finders is effected. .In the drawings g: 1 shows circuit arrangements for a line finder and its-allotter. Figs, 2a and..2b show the terminal connections .ior two and three allotter per group respectivel and Fi 3 shows modifications required inFig. l Where the line finder is oneof a number of graded findersconnected to a. single first selector.

Reference will first be had to Fig. l. The line finder is @2 0 outletsingle motion hunting switch driven by an individual electric motor thecircuit of which is controlled by a latch magnet which, on operation closes the circuit for the motor and removes a. latch from one of the gear wheels. s t h s urnished with fiwipers and associated arcs of contacts, the, Wipers being paired and p s tion d s that when one wiper or alpair le s the l st on acts in its. are the other wiper steps on to the first contact in its associated arc.

+, -S and p respectively, being shown at theright handof. the drawings. On theleftof the drawings is shown aline circuit with its connections over .ar distributing frame designated IDF to asubscribers line SLand to the terminals FS of this line in the final selector multiple. Below the line finder is'shown the allotter which is of similar construction to theline finder but which has only1100 outlets from its16 arcs of contacts; Its wipers which are also paired' are designated Al to A8. Therelays: shown in this part of the figure serve for1thecontrol-ofthe allotter, and line finder. To the left of therelays is shown a set of 9 terminals which provide for the starting of an allotter, the selection. of the setgof .wipers onthe linefinder to beused and the extension of the start circuit to, another finder should the one shown be faulty andror routine testingpurposesn i The ap aratus shown will now be referred to; In the line circuitis shownpthe line rela-yLgcut oif relay K and meter MTR. Contacts; of the line relays of one sub group of 100 lines are cone nectedto ,a common start relay. designated S, and similar contacts of the line relays of the other sub-group ofl00 lines 'ofthe same 200-line group are to be assumed connected to another start relay. Only the starting arrangements relevantto the first sub-group are shown in;detail, the arrangementsofthe other group being similar. ;They willbe referred to where necessaryvas the description proceeds, There isfalso a relay RT for automaticsroutine testing purposes. 7

The line finder comprises thewipersand banks before referred to, the latch magnet FMU for controlling the driving motor, two, switchingrelays HA and HB, one for each sub-group oflines and themetal rectifier MRA. The allotter. circuit includes the allotter latch magnet AMU, start relay ST, wiper switchingrelay WS, allotter test relay vT and its auxiliary relay TA, finder: test relay P and its auxiliaryPA, last contacttrelay LC, and off-normal contactsON. There.is also a pairiofrelays designated SA: and ZA whichare concerned with atimingl circuit for extending the start wire if the allotter does notoomplete its task within a predeterminedtime. The outlets the starting condition. It will, ho wever, for the purpose of-description be assumed thatthelink inlthe bank of the allotter. are nultipledover all the allotters on thepanel, i.- e. they are connected to all the finders on the rack and 30 outlets remain over for connection to finders on other racks if necessary as previously explained. The contacts in the arcs associated with the pair of wipers designatedAB are not multipled but con tacts associated with outlets to alluthe finders of a group towhich' the .allotter is assigned are commoned and connectedto an earthterminal on the allotter. Wiper A8 is connected in the allotter test circuit so that test for a free" line,

finder can only be made amongst those serving aparticular group of lines asdeterminedby' the strapping and earthing of the-contacts in the arc associated-with the wiper. The off-normal contacts ON are only open when the allotter wipprises 52contacts, the 52nd contacts beinglast contacts to which line finders are not connected, only50 of thecontacts being'used'for outlets. If a pair of arcs associated with a pair of wipers are considered as comprising contacts I to 52, represented by the full line semi-circle and contacts 53 to lM representedby-the dotted semicircle, contact I in the arc of wiper A8 is directly earthed and contact I04 is earthed over contact lcl when relay LC isoperated; Contact linthe arc of .wiper Al is connected to .batteryover contact pa3 for a purpose which will. be madewclear. later. Included in the allotter circuit is acontactdesignated $30 for. causingthe allotter to execute a further'search if after a search line finder has been found free. Both theallotter and the line finders are high speed switches. driven atthe rate of about 200 steps a second; Jacks J are provided for testingpurposes. I

The operations involved in extending a call from a calling line to a group selectorwill now be described in detail. i

The .allotter normally stands on contacts con nected to an outlet to a free finder-selector link, and if this link is free when the startcircuit is closed it is seized for the call that gave rise to on .the outlets to which the allotteri is resting is busy. When a subscriber initiates a call; line relay Loperates in a circuit from earth over'conr tact k2, the calling loop, contact lcl, winding. of the relay to battery. Contact ll connectsnearth to the start Wire common to the sub-group,- which in the present case will be taken to be the. subgroup having the common startrelay 8- associated with it. Contact Z2'c0nnects battery over -a suitable resistance to the contact in the arc of wipers F3 associated with thecalling line and connected to wire m, contact il3aearths the test wire p in the final selector multiple and contact. Z4 opens a point in the meter. circuit. Relay 3 operates over the start wire and contact ll. .Contact .sl connects earthto terminal SI which is extended by strapping to terminal Wand over contacts zal, wsl, relay ST, contact 2114 to battery, and

contact 32 disconnects batteryfrom the first con-wv tact in the arc of wiper F3 This battery connectionis provided in order tosto-p the line finder in that position should the calling conditiorr'be .removed before search hasbeen completed. Re-

lay ST operates and closes the following circuit; earth over contacts tLtal, stl magnetAMU to battery. In addition circuits are prepared as follows: at contact st2 for the upper winding of relay; TA, at the moment short-circuited over contacts operate as wire p will be earthed and magnet AMU will beenergised to start the motor and the switch-will commence to drive. When-a free As the outlet to which theallotter is con- .nected is assumed to be busy, relay T will not finder in the group of finders to which the allotter is restricted in its search is found, relay will operate to-stop-the .allotter. The circuit tor relay T is from earth over terminal E. the commoned contacts the marking are, wiper A8, rectifier MRB, both windin s of relay 1', contact st3, wiper A1, contacts. hafi and hbfi, wire 73 to battery connected to this wire in the asso-' ciated group selector. Relay '1 holds to this bat.- tery over its lowv resistance left-hand winding and earth over contact ti, thereby mark-ing the finder selector link busy, disconnects the direct earth from magnet and switches relay TA into circuit with magnet AMU. Theresistance of the circuit including-the winding, of relay TA is too hi h to permit the, magnet to remain operated and the magnet is tie-energised and the switch brought to rest.

If the allotter fails to find a free finder in the group assigned to it before reaching the end of the bank, it will continue to drive over the whole of the bank so that. any free finders connected in the multiple to contacts situated between contact .l and the contact from which the search started may be seized. When the first contacts are reached contacts ON open and the shortcircuit across relay LC is removed. Relay'LC operates and at contactlcl connects earth to the last (104th) contact in the arcs ofwiper A8 so that if drive continues until this position is. again reached, relay T will operate from the earth over contact Zcl to battery over the wiper A1, contact 81) and .the lower winding of relay TA. Contact tl opens to disconnect the circuit of magnet AMI] and stop the switch. The two windings of relay TA are connected in opposition so that when both are energised as they will be in the event now under consideration, the relay will not be operated. Contact sp is opened every second by a suitable timing'device and when it opens, relay T releases before relay TA can operate and the switch is driven off to make another search for a free outlet. 3

Continuing with the description of the normal operation of the circuits, it will be remembered that when a free finder was found by the allotter, relay T operated and connected relay TA in series with the alotter magnet AMU. Relay TA operates in series. with the magnet winding and at contact tal substantiates the starting earth holding relay ST operated. Contact 'taZI .closes without efiect in the present, example and its purpose will be referred to later. Contact 1M3- prepares a circuit for the finder test relay 1, contact m4 prepares a circuit for the finder switching relay, contact :ta5 applies earth tothe negative wire to operate the impulse relay of the group selector which in turn operates the usual release relay for holding the connection by applying earth to wire 11, contact me closes a circuit from earth over contacts pl, pat and wiper A6 forv magnet FMU and contactv ta'l opens the operating circuit for magnet AMU. In consequence of the application of earth in the group selector to wire p relay T is short-circnited and released but relay TA is guarded by the open contact tal. Magnet 'energises and .bringsabout the driying of the line finder in search of the calling line. When this is found, relay P operates in a circuit irom earth over the relay winding, contacts m3, wsZ, wiper AI, F3 wire m, Contact 12 .to battery. Contact pl switch srelay PA into the circuit of magnet FMUL The left-hand winding of "relay PA .of high resistance and the relay operates over this winding but the magnet will not hold and the switchis therefore stopped. Contact pal closes a circuit from earth over contacts m4, ws3, wiper A3 for relay HA, contactpM prepares a'circuit formagnet AMU over the .low resistancerighb handwinding of relay PA, contactpaiconnects battery to the first contact in the are associated with wiper A] for a purpose to be described. Contact pa! substantiates contactsts, contact pa-S short-circuits relay ST to force its release should another call have been initiated and contact m6 opens .a further point in the circuit for magnet EMU shunting the left-hand winding of relay PA.

Relay HAoperates and locks to. wire 11 at contact haL. Contacts M2, M3, had extend the negative, positiveand test wires from the group selector back to the line circuit over wipers Fl, F2 f and F3, contact 11115 applies earth to wiper F4 to operate cut-off relay K over wire p and contact hai disconnects battery over wire pb-irom wire -92.

Relay K operates and disconnects the line relay L at contacts kil and M. The cums relay remains held, over wiper F4 to the earth on 'wire p. Relay L releases, removes the starting condition from the start wire so far as this-call is-concerned,

connects up the meter and extends the-earth applied in the group selector to wire p in the final selector multiple to maintain the busy marking on the line contact therein. Following the operation of relay PA, relay ST releases by reason of the short-circuit across it and relay P releases by reason of the short-circuit applied over contact ha l. Release of relay ST releases relay'T-A at contact st! and the holding earth for relay ST at contact tal is removed. The following circuit is now closed: earth over contact tl, ta'l, st I, p112, low-resistance right-hand winding of relay PA, magnet AMU' to battery. The magnet operates and the switch drives until a freefinder selector link is encountered, marked in the arc of wiper 40 A! by battery overcontacts has, 71.116 and wire pb,

whereupon relay T operates to stop the drive. This selection of a free link can only take place amongst finders of the group with which the allotter is concerned as determined by the strapping of the contacts in the arc associated with wiper A8. Relay TA will not operate as its circuit is open at contact st2. Consequent on the opening of the circuit of the alotter magnet, relay PA included in this circuit releases and opens the test circuit at contact pa4 thereby leaving the al-lotter standing on the selected outlet without operating thev finder thereof. When contact pa! opens, relay ST is freed for operation if another call is waiting or when a new start condition is applied. If the allotter is unable to preselect a finder in the group assigned to it, it continues in rotation'unt-il th first contacts are reached whereupon a test circuit will be completed and the switch stopped. This circuit extends from earth on contact I in the arc of wiper All, the wiper rectifier MR3, :both windings in series .of relay T, contact pad, wiper A l, first contact in its arc, contact 110.3 to battery and the allotter stays onthose contacts until it is wantedior another-call. Relay T is released when relay PA releases following the operation of contact til.

When the allotter is first taken into use and relay ST is operated, contact 5155 connects the left-hand winding of relay SA to wire Wires AS and AZ are connected momentarily to earth periodically by a timing device there being, an interval of 6 seconds between the earthing of wire AS and that of Wire AZ. When wire .AS. is

relay ZA to wire AZ. If relay ST is still operated at the expiration of 6 seconds from the operation of relay SA, earth applied to wire AZ operates relay ZA and this relay locks up in the following circuit: earth overthe contact inthe other or one of the other allotters associated with the same group of lines and corresponding to contact m3; terminal ZZ, contact 2113 of the allotter the operation of which is being described, left-hand wind ing of relay ZA to batteryandin parallel therewith over lamp ALto battery. The lamp glows to in'dicatea condition of failure by theallotter to complete itstask and contacts an and eat of relay ZA transfer the starting circuit to the other or to a spare allotter. Contact zal opens the start wire and releases relay ST and contacts m5 and 2116 complete circuit for alarm and supervisory signals. It will be noted that if, before a calling line hasbeen found, another call in the same subgroup of'llnes occurs, relay S will remain operated and the start condition will "be 1 maintained. floweveniconsequent on the findingof a calling line'bythe finder, relays? and PA are operated and the latter by short circuiting relay ST at contact 110.5 ensures release of relay'ST so that relay SA will be' released'at contacts st5 in readiness foranew timecycle. i I a If a line in the other hundred sub-group of the 200. line group calls; another start relay will .be operated in the same manner and perform like functions. to relay S. Its-contact I will connect earthto terminal SII'which will be connectedin the second. allotter of the group-associatedwith the line group inquestion' to the terminal YZ. If theallotterof Fig; 1 is now assumed to be one normally taken into use forcallsin this other sub-group, the earth. over terminal SII. will be extended via terminal YZ, contactzaz', relays WS and ST to battery; Relay ST will operate and if necessarystart the allotters in search of alfree outlet. Relay WS on operation changes the conand ST. The ZZterminals on the twoallotters are strapped together; If the allotterI should fail and relayZA be operated, a call signalledover terminal SI "is extended over terminal contact z'al land terminal WXO inallotter I, the

strapping, Fig." 2a, to terminal WX in allotterlI and thence to the ST relay of that allotter. Simic larly if allotter II should fail and its'relay ZA be operated a call signalled over terminal SlIis extended over terminal YZ (column 11),, contact zaz 'aridterminal YZO in allotter II, thestrap Ding. Fig. Zato terminal YZ in allotter I and thence to relays WS and ST of that allotter. 'If there arethree allotters per group of lines, the arrangements shown in Fig. 21) may be used: In

thisarrangeinent calls are normally dealt with as the case may be, to the group selector and the" allotter was releasedfi The group"selector and subsequent selectors are set by impulses from thesub'scribers diarandthe wanted line tested and iffree run'g. Whenthecalled subscriber nections fromwipers Ali and A3 to wipers A2 and 'A4 so that thecalling line will be searched for over wipers F5--F8 the test circuit being inthis instance overflrelay P, front contact wsZ, wipers A2, F1 and wire m. When the line isfound and relay PA i s operated, switching relay HE is operthis relay performs functions similar to those per'- formed by relay I-IA for callsin-the other hundred sub-group. {It-will be noted. that when relay TAlis operated contact 1302 extends the. earth It may here be co nvenient to refer to Figs. 2a

uated over. wiper A4 and front contact ws3 and and 21). Fig. 2d,shows, the terminalstrapping employed when there are two allotters per group o fjlines 'The terminalsSI, SH and so onpcorrespend toLthe'terminals similarlydesignatedein Fig. 1,those terminals in the column headed I being ation in" response to calls signalled over terminal response to ans signalled over terminal SII. It will be seen that for a call signalled over terminal SI the earth on that terminal is extended to replies, a"positive battery, the negative pole of which is earthed is connected at the feeding bridge circuit to wire p and the callers' meter is oper ated over wiper F3 or F1,wire m, the'meter MTR;

contacts 14' and k2to earth. The cut-'ofi'relay K remains held over-wire '17 and "wiper F4 or F8 in an independent circuit over contact [72:15 or hb 5. At the end of the conversion the caller clears, releases the impulse'relay at the feed ing "bridge which in turn releases the slow-torelease release relay. :This latter relay disconnects earthfrom wire 'psrelea'sing" the operated switching relay in the line finder and removing e the busy marking from the contact in the are of wiper A1. Release of the switching relayreleases relay K which restores the: connection of the line relay L to the line. i: l

If the group selector is one arranged to connect battery potential to the test wirewhen it is free, theconnection over contacts hat? and M76 and wiremb would be omitted and contactshafi and M26 will be connectedin seriesbetweenthe contact in the arc of Wlp8l,A1aI1d wire pat the place indicatedby the broken; wireBP. When calling line is ioundandthe switching relay op erated, the test circuitforrelay T will be opened thus guarding the outletagainst seizure-by an allotter. i 1 If the line finder is one of a number of vgraded finders, thatis if a number of finders in different those, of one allotter adapted normally for operterminal WX-in allotter I and thence, by reference to Fig. 11, to relay s71; Similarly for a call signalled over terminal SIIQ the earth on that terminal isextended to terminal YZ in allotter II groupsare connected to the same group selector, the test circuit for the allotter may be arranged asshown inFiga 3: .In this figure the terminals corresponding to P andPB inFig. 1 are shown for three line finders LF and in addition a terminal PA is provided on each'finder. All; the ter .minals P of thegraded line finders are com-' .moned andqconnected to the selector test wire to which earth is adapted. to be connected in the group selector GS and battery is connected'inthe group. selector GS tol terminal PB of one of the finders and extended over chain contacts of the and thence, byreferenceto Fig. 1, to relaysWS switching :rel'ays of all the lgraded' finders to the finder test "wine. The allotter test *circuit extends lower terminal P, the Istrap to terminal PA of the Efinder :shown uppermoshthe serially con-- nected switching relay contacts of alltthe finders to the battery connection to terminal PB in the group selector. This chain circuit is opened by the operation (of the switching relay in. any one of the finders.

If some 1015 the ifinders of a grouplare igraded, the ungraded finders will be connected to earlier contacts ithe allotter bank than the graded finders and only the "outlets the arc of wiper A8 corresponding to ungraded finders -iwilllceconnested to earth. The outlets corresponding to graded finders will bo-connected tolthelast contact in the pair of arcs (the l04th) and contact 'lcl. inrsearching for zairee finder, all the iungraded rfinders must be tested before the graded finders as it is only after the switch has passed. over its first contact position that the marking for graded :finders will be connected up by the operation :of relay The lirreilmler shown in Fig. l is arranged for self-routining. (I-f the upper springs of jack'Jl are bridged rlzy a plug, a start condition is simulated; relay :RT operating serie with relay 6 trots-em t hoonnected to the deck. The 'allotter will take into :use -a free line find-er and, provided no other calling condition the subgroup is present, "the 'rfinder will rotate to -a last contact position in which relay P-yvill be operated over wipers Al and E3, contact rtl to battery. The last contacts on :the other dine finder arcs, except the mccfwtperF-l, are unconnected. Following the operation of relay PA and release of relay S'I theallutter will advance to the next free outlet-available to=-itand the line ".finder o'f this-utlet will ibe rotated in like :manner. When the allotter moves on after-the line has :been stopped --'on last contacts, the switching relay operated will bereieasedas no earth oe presenton wirep; in this manner a'rlldihe line Efinders of the :group may be tested automatically. 'If the tack d2 be -plugged, an indication 'will'lie given by the closure of "contact 7th.! that the set "of wipers B'5-'-:'F8 is in'use. A "similar test for "lines in the 'other'sub-Lgroup mayb'e had lay bridging the lower springs of jack .lll.

We claim:

:1. In a telephone system including :a plurality of 'of incoming llinses, s plurality of call finders :f'or reach of said groups ihavmg access to all of the lines inthe' group, a call allotter assaid call allotters toa-llocate calls only-to sociated each group of lines having circuit paths to all of said cal-1 finders, means respon- .sive to the "initiation of a call :over one of said lines' fo'r starting the :associatedcall alldtter, and means causing said associated call allotter to "al loeate said call to a call finder in the group having access to said one line.

an a telephone system including a plurality of groups of incoming lines, a plurality of call .firrders for each of said groups having access *to all of 'the lines in the group, a, call allotter associated each group of lines having circuit paths to all of-saidpallfinders, means responsive to the initiation of a call over 'one of said lines -for starting the associated call aillo'tter, and means preventing said associated call allotter iro m allocating said call to 'callfin'ders which do nut have access-to said one line.

3. In a telephone system "including "a group of finders, connections therebetweencapable of :providing access to all of said-callfindersi-rom each of .said call tallotte'rs, and means causing-each of a pare ticular group of said cal1wfindersp .4. In atelephone system including -a rackcon- 'taininga plurality of panels of call finders and-a panel of call allotters, a series of first :multi-ples each common to all of thecall finders" in one panel, -a second multiple between (some but not all of said first multiples, a third: multiple com-: mon to all of :said'callallotters capable of providing access'to all oi said cell finders drown any one of said call allotters-and means causing any one of said call allotters to extend connections over said multiple-only toparticular panels of call finders operating on common first multiples. i i I v 6. In a telephone system including =a. plurality of racks :each containing a ,pluralityof :panelsof call filldels and a panel of -cal1-:a:llotters,-a

series ei first 'multiples each common ito all of in diiierent iiack s, is third multiple common to all cf the call ai-lotters in one rack 'rapal'ile of providing access to ailor the call rfin'dersin said one rack and also capablerof providing access to all of the call :finders in other. racks which have their firstmultiples commoned to the first multiples of call finders in said one rack, and means causing anyone of said can allotters in said one rack to extend connections over said third multiple only to particular .zpanel's of call finders operatingon common lfirst multiples. fi. A telephone system as claimed 'in"cl'airn 3 inclu'ding'a test circuit in each of said call "allotters, and said means comprising a marking bank individual to each"-o'f said call allotter -and.

said groupsof call finders and causing thesev-- eralsub clivisions to "be served by different call =allot'ters, a normally inactive "call allotter assoc ated with each such 'groupp and means responsive to a failure of one of the call allotters "serving a sub-division of a group to cause thesaid associated normally inactive call allotter to act as an alternative for said one callallotter.

9. A telephone "system as claimed in claimv 3 including meanscausing'oneof said call allotters to pre-selec't an idle call finder in the .said .par-

ticrular group in which it is permitted to allocate ca ls. 11). In a, telephone system as claimed in claim 3 in which one of sai'dgroup's of call finders is subdivided into'first choice and second choice finders,

means preventing the call allotter serving said call nll'dtters and a plurality of groups of call .1; ifinders,a test circuit included in the call allotter in which said means. comprises a marking of terminals eachcorresponding to one of the call finders to which the associatedrcall allotter is circuit for ach call allotter including a number capable of allocating calls, and means for marking particular ones of said terminals to determine the group to which calls may be allocated.

DAVID ADAM CHRISTIAN.

DOUGLAS PERCY LONG. 

